This invention relates generally to locking pliers and, more particularly, to an improved release mechanism for such pliers.
Pliers-type hand tools with toggle-locking mechanisms are generally known as locking pliers. These pliers usually comprise a fixed handle having a fixed jaw on one end thereof. A movable jaw and a movable handle are pivotal relative to the fixed handle to open and close the jaws. To operate the pliers the movable handle is closed relative to the fixed handle to close the jaws and seize a workpiece firmly therebetween. The handles are then tightly compressed such that the toggle mechanism locks the pliers onto the workpiece. The pliers will remain firmly locked in place without the continuous application of force by the user.
The pliers may comprise a relatively simple toggle-locking mechanism where a single link has one end pivotably connected to the movable jaw and the opposite end adjustably and pivotably received in the movable handle such as shown in U.S. Pat. No. 4,546,680. The pliers may also comprise a more complex toggle-locking mechanism that uses a compound linkage where multiple links are pivotably connected to one another between the fixed handle and the movable handle such as shown in U.S. Pat. No. 5,056,385. The locking pliers may also comprise self-adjusting pliers such as shown in U.S. Pat. No. 6,941,844. Other embodiments of locking pliers are also known.
Adjustments in the force applied by the jaws to the workpiece are generally made by turning an adjusting screw mounted in the fixed handle that engages the toggle locking mechanism. The adjusting screw is translated relative to the fixed handle to modify the physical dimensions of the toggle mechanism. This adjustment varies the distance between the jaws and varies the force applied by the jaws to the workpiece when the tool is locked. In certain applications the forces on the pliers can be very high.
Because an over-center locking mechanism is used, once the pliers are locked in position they cannot be opened by a force applied to the jaws. The pliers can only be released by a force applied to the links of the locking mechanism. This may be accomplished by pulling the ends of the handles apart from one another. If the locking force is great, a significant force must be applied to separate the handles and open the pliers. To make opening the pliers easier a release mechanism has been developed. The release mechanism typically comprises a lever pivotably connected to the movable handle at a pivot pin such that the first end of the lever is disposed between and is contacted by a link of the locking mechanism and the fixed handle when the jaws are in the closed and locked position. By pushing on the opposite end of the lever, the lever pivots about the pivot pin forcing the first end of the lever away from the handle to release the locking mechanism.
One problem with such an arrangement is that because the release lever is disposed between the handle and a link of the locking mechanism, the dimensions and configuration of the release lever and its location within the handle changes the geometry of the locking mechanism. A change in the geometry of the locking mechanism changes the locking characteristics of the pliers. As a result it is necessary that the dimensions and configuration of the release lever, its location in the handle and its engagement with the locking mechanism must be carefully controlled during manufacture of the wrench. The controls required during manufacture and assembly of these components increase the cost and complexity of manufacturing of the wrench.
Thus, an improved locking mechanism for locking pliers is desired.